Accessing states of an Akka Actor through messages - scala

Question

I'm trying to access the state of a particular actor through messaging. What I don't know is how I can retrieve the state of the actor. Here, I need to access the state variable of Node, state1. I want to avoid using promises/futures in the code. How should I go about modifying this code if I want to do that?
class Node extends Actor {
val state1:Int = 4
def receive = {
case getState => {
sender ! ??? //How should I send the 'state1' to the sender?
}
}
}
class Master extends Actor {
def recieve = {
case someCase(node_actor:ActorRef) => {
// My aim here is to get the "state1" from node actor into var 's'
var s:Int = node_actor ! getState
}
}
}

Answer 1

Actors are designed perfectly to avoid manual handling of scala.concurrent. things.
Just separate request and response handling into different receive cases:
class Node extends Actor {
import Node._
val state1: Int = 4
def receive: Receive = {
case getState =>
sender ! State(state1)
}
}
class Master extends Actor {
import Master._
def receive: Receive = {
case Action(node) =>
// My aim here is to get the "state1" from node actor into var 's'
node ! Node.GetState
case Node.State(state) =>
// do something with state
}
}
object Master {
case class Action(node: ActorRef)
}
object Node {
case object GetState
case class State(state: Int)
}
Sometimes you could have also some intermediate values calculated and don't want to do something until you'll get the answer but being unreachable also is not acceptable. So you could just wait for node response in separate Receive while stashing incoming messages, like this:
class Master extends Actor with Stash {
import Master._
def receive: Receive = {
case Action(node) =>
val intermediate = scala.util.Random.nextLong()
node ! Node.GetState
context.become(waitingForState(calc = intermediate), discardOld = false)
}
def waitingForState(calc: Long): Receive = {
case Node.State(state) =>
// do something with state and calc
context.unbecome()
unstashAll()
case _ => stash()
}
}